Current all wheel drive (AWD) vehicle drivelines may comprise a primary front drive axle coupled to a secondary auxiliary rear drive system. The secondary auxiliary rear drive system typically includes a power transfer unit, a drive shaft, an AWD coupling device, a rear axle, and rear half shaft assemblies. When the vehicle is operating in a 4×2 mode, the front primary axle provides tractive forces to keep the vehicle moving, and to overcome the driveline efficiency losses of the secondary drive axle that is being driven through the tire/road surface interface. The driveline efficiency losses are largely due to oil churning losses, viscous drag, inertia, and friction.
To provide a more fuel efficient driveline for operating in 4×2 mode, it is desirable to have the ability to completely “idle” the secondary auxiliary drive system by disconnecting the secondary auxiliary drive system from the primary drive system and allowing the secondary auxiliary drive system to rotationally coast to a stop. Idling the secondary auxiliary drive system in this manner would remove virtually all of the driveline efficiency losses from the secondary auxiliary drive system with the exception of its non-rotating inertia.